Airline alert as volcano spews ash into sky

A VOLCANO in Alaska's Aleutian Islands has sent up an ash cloud that is prompting scientists to increase the alert level for commercial aircraft traffic.

The Alaska Volcano Observatory said satellite images showed Cleveland Volcano had spewed ash 4572 metres into the air in a cloud that moved east-southeast.

US Geological Survey scientist-in-charge John Power called it a small explosion.

"It's not expected to cause a disruption to big international air carriers," he said.

But the event drew strong interest from air carriers.

"Any time you put an ash cloud up into the atmosphere, the airlines, the air carriers, air freight companies - it's a major concern," Power said.

The ash cloud was significant enough to raise the alert level from yellow, representing elevated unrest, to orange, representing an increased potential of eruption, or an eruption under way with minor ash emissions or no emissions.

Cleveland Mountain is a 1729-metre peak on uninhabited Chuginadak Island about 1512 kilometres southwest of Anchorage.

The US Federal Aviation Administration and the airline industry becomes concerned for trans-Pacific flights when an ash cloud has the potential to exceed the 6096-metre threshold, as Cleveland Volcano has done in the past.

Cleveland Volcano's last major eruption was in 2001. It has had bursts of activity nearly every year since then, and the ash cloud Thursday was not out of character.

"It's not unexpected for a volcano like Cleveland to do things like this," Power said.

"Unfortunately, Cleveland is one of those that is so remote, we have no on-ground monitoring or instrumentation there, so it's hard for us to pinpoint things any more accurately than we can do with satellite imagery."